I also like playing tug with my dogs. To me it is a cooperative game. (cooperative "killing.") LOL. I have rules: No teeth hit my skin, No leaping up and grabbing the toy from my hand, and the dog must "give" or "out" when I ask. (teach that as a seperate lesson first before playing tug. Trade for a treat, give back the toy, repeat. Add the cue word)
If the dog brings me a toy and asks to play, I play if I feel like it and don't if I don't. To me it's just like a friend asking me to play a game. I might and I might not. Jose brings me a tug toy often, drops it at my feet and backs up, wriggling all over. He's asking if I want to play. So, if I'm not busy, I say, "sure...let the games begin." So, as far as always being the one to instigate it, I don't agree with that one. But he must let go when I ask.
I let the dog win lots of times. I believe this builds confidence in a dog and I like a confident dog. Confident dogs are less apt to have behavior problems than insecure dogs. My son's dog, who was abused as a pup would never have dreamed of playing tug in the past. She now gives it all she's got. And I like to see that. It means she trusts the person she's playing with not to hurt or scold her. She has gotten 95% more confident in herself. That is one exercise we play with her a lot.
It's also a game dogs play with eachother. So, the old myth that it "teaches opposition," I don't buy. It's a game, pure and simple. But games have rules.